Various optical/flow systems employed for transporting a fluid within an analytical instrument to an imaging and optical analysis area exist in the art. A liquid sample is typically delivered into the bore of a flow chamber and the sample is interrogated in some way so as to generate analytical information concerning the nature or properties of the sample. For example, a laser beam may excite the sample present in the bore of the flow cell, and the emitted fluorescence energy provides signal information about the nature of the sample.
If the system is designed to handle a sparse sample with a wide range of particle sizes within it, the flow cell may be rectangular in dimensions and the laser excitation will consist of a fan of laser light rather than a beam of light.
The inefficiencies of standard methods of collecting light from a rectangular flow cell with laser fan illumination can result in weak particle fluorescence which varies greatly with particle position within the flow cell due to the sensitivity of the optics to different optical paths taken by the light on its way to the detector. This poor signal quality is accompanied by high autofluorescence from optical components in existing instruments. Therefore, there is a strong need in the art for an effective way to improve sample fluorescence signal quality and to reduce the background fluorescence level.